The present invention relates to a monomer containing an electron-withdrawing group and an electron-donative group and a copolymer comprising and a proton-conductive membrane comprising same. More particularly, the present invention relates to a polyarylene-based copolymer useful as a proton-conductive membrane which can be used as electron for primary battery, electrolyte for secondary battery, high molecular solid electrolyte for fuel cell, display element, sensor, signal transfer medium, solid capacitor, ion exchange membrane, etc., a monomer to be used for the copolymer, and a proton-conductive membrane comprising the copolymer.
Electrolytes are usually used as (aqueous) solutions in many cases. In recent years, however, there is a growing tendency to replace such aqueous soluble-form electrolytes with solid electrolytes. The first reason for this is the easiness of processing in applications of solid electrolytes to, e.g., the electrical/electronic materials mentioned above. The second reason is the trend toward reduction in weight, thickness, length and size, and toward energy saving.
Conventionally known proton-conductive materials include both inorganic materials and organic materials. Examples of the inorganic materials include uranyl phosphates which form hydrate. However, these inorganic compounds are insufficient in interfacial contact to pose many problems concerning the formation of a conductive layer on a substrate or electrode.
On the other hand, examples of the organic compounds include organic polymers such as polymers belonging to the so-called cation-exchange resins, e.g., sulfonated vinyl polymers such as sulfonated polymers with perfluoroalkylsulfonic acid represented by Nafion (manufactured by E. I. Du Pont de Nemours and Co., Inc.), and perfluoroalkylcarboxylic acid polymers, and polymers prepared with incorporating sulfonic acid groups or phosphoric acid groups into heat-resistant polymers such as polybenzimidazole and poly (ether-ether-ketone)s [see Polymer Preprints, Japan, Vol.42, No. 7, pp. 2490-2492 (1993); Polymer Preprints, Japan, Vol. 43, No. 3, pp. 735-736 (1994); and Polymer Preprints, Japan, Vol. 42, No. 3, p. 730 (1993)].
These organic polymers are usually used in the form of a membrane. A conductive membrane made of these organic polymers can be bonded to an electrode while taking advantage of the solvent solubility or thermoplasticity. However, many of these organic polymers have the following problems besides being still insufficient in proton conductivity. The organic polymers deteriorate in durability or in proton conductivity at elevated temperatures (100xc2x0 C. or higher). The organic polymers show drastic deterioration of dynamic properties, particularly elastic modulus. The organic polymers have a great dependence on humidity conditions. Further, the adhesion of the organic polymers to the electrode is not fully satisfactory. Moreover, the conductive membrane swells excessively during operation due to the hydrophilic polymer structure, and this swelling leads to a decrease in strength properties or a deformation. Consequently, application of those organic polymers to the aforementioned electrical/electronic materials and the like pose various problems.
U.S. Pat. No. 5,403,675 proposes a solid polymer electrolyte comprising a sulfonated rigid polyphenylene. This polymer is produced from a polymer comprising a phenylene chain obtained by polymerizing an aromatic compound (the polymer structure is described in column 9 in the specification) by reacting the phenylene polymer as the main component with a sulfonating agent to incorporate sulfonic acid groups thereinto. However, the incorporation of a large amount of sulfonic acid groups results in a sulfonated polymer having considerable deterioration in mechanical properties that exhibits a deteriorated toughness and thus can crack although proton conductivity improves with the increasing amount of sulfonic acid groups incorporated. Therefore, it is necessary for the polymer to have a desired toughness, maintain proper mechanical properties and be adjusted to a proper sulfonation that realizes a desired proton conductivity. In fact, this polymer undergoes sulfonation too much and thus can be very difficult to have a proper control over the amount of sulfonic acid group to be incorporated therein.
The invention has been made under these technical circumstances.
Accordingly, one object of the invention is to provide a polyarylene-based copolymer which can be easily controlled in the upper limit of the amount of a sulfonic acid, which impairs the mechanical properties of a copolymer, and can provide a sulfonated polymer that forms a proton-conductive membrane having a high proton conductivity over a wide temperature range, an excellent mechanical strength and an excellent proton conductivity and showing inhibited swelling in hot water and an aqueous solution of methanol.
Another object of the invention is to provide a novel monomer to be used in the copolymer.
Still another object of the invention is to provide a proton-conductive membrane comprising the copolymer.
The foregoing aim of the invention will become apparent from the following detailed description and examples.
The invention provides a monomer containing an electron-withdrawing group and an electron-donative group represented by the following formula (1): 
wherein Y represents a iodine atom, chlorine atom or bromine atom; X represents an electron-attractive group; B represents an electron-donative group; and Z represents a group represented by the following formula (2-1) or (2-2) or a monovalent condensed ring hydrocarbon group: 
wherein D represents an electron-donative group or single bond; R26 and R27 each represent a hydrogen atom, alkyl group or aryl group; and q represents an integer of from 1 or 2.
The monomer represented by the formula (1) is preferably 2,5-dichloro-4xe2x80x2-(4-phenoxyphenoxy)benzophenone.
The invention also provides a copolymer containing a repeating structural unit represented by the following formula (3) (hereinafter referred to as xe2x80x9crepeating structural unit (3)xe2x80x9d) in an amount of from 5 to 95 mol % and having a weight average molecular weight of from 10,000 to 1,000,000: 
wherein X, B and Z are the same as defined in the formula (1) above.
The copolymer of the invention preferably contains a repeating structural unit having a flexible structure in its main chain other than the repeating structural unit represented by the above formula (3) in an amount of from 5 to 95 mol %.
The copolymer of the invention may further contains a sulfonic acid group in an amount of from 0.5 to 3 mg equivalents/g.
The invention further provides a proton-conductive membrane comprising the above-described copolymer containing a sulfonic acid group.